Geotechnical Investigation of the Mount Polley Dam Failure

In August 2014 the Mount Polley mine tailings dam failed in the Cariboo region of British Columbia, Canada, resulting in a catastrophic release of stored tailings and water. KCB was retained by the British Columbia Ministry of Energy and Mines to investigate the geotechnical reasons for the dam’s failure. The six-month forensic investigation included a site investigation and laboratory tests, and review of the related engineering, construction and operational records.

KCB’s findings formed part of the Independent Review Panel’s Report on Mount Polley Tailings Storage Facility Breach published in January 2015. The results of KCB’s work provided the basis for understanding how the dam failed, and will also be an essential reference for the future design of tailings facilities in B.C.

Challenges

  • Plan a forensic geotechnical investigation at the site of an active emergency response
  • Determine geotechnical causes of the dam failure

Solutions

  • Mapped geomorphology of failure area
  • Completed geophysical surveys of foundation in failure zone
  • Sampled undisturbed and disturbed foundation soils and dam fills
  • Completed in-situ standard penetration, cone penetration and vane shear tests
  • Installed instrumentation to measure water pressure and movements in foundation soils
  • Completed over 1,000 soil index property tests
  • Completed over 50 advanced soil strength and behaviour tests

Successes

  • Improved geological knowledge of area
  • Identified physical properties and mapped extent of overconsolidated glaciolacustrine clay unit (Upper Glaciolacustrine Unit or UGLU)
  • Identified location of failure entry and exit, and sequence of dam failure
  • Determined failure mechanism as a foundation sliding failure through the UGLU
  • Investigation findings helped to revise Health, Safety and Reclamation Code for Mines in British Columbia